Nope "she" was just getting a bit of a workout... Those black flakes on your arms are most likely unburnt powder from blow back during firing. If you shoot, oh say 500+ rounds in todays class, your forearms will be dirty, as will your hands. Most people shoot FMJ, which really means the back of the bullet has exposed lead while the rest is covered in a thin copper jacket. When you fire your gun a small amount of that lead is aerosolized during the powder ignition and consequently end up on your hands and all over your arms. That, an unburnt powder and carbon from act of firing. If you are not paying attention and then eat something your fingers have touched, you will be digesting lead and other junk. You will breathe it too. That is why you should shoot in a well ventilated indoor range or outside, and always wash your hands before you eat after shooting! You see a lot of guys wipe their face and they are smeared with carbon or blow their nose after a range session and it is blackened with all the dust you have been breathing!
TMJ or Total Metal Jacket is completely encased in copper. This helps mitigate lead exposer. There is also lead in the primer i read somewhere... They also make lead free ammo. I think Clint at Thunder ranch requires ammo that is lead free. Its a good idea, but it is expensive. When you shoot a lot, or are around people shooting often, you might be surprised you have elevated lead levels in your blood. Lead acetate tastes sweet. If you are ever at an indoor range and leave with a weirdly sweet taste in the back of your mouth it may be lead. I notice it after pro longed indoor range sessions, i have never noticed it shooting outdoors. See so you learned something today and i got up early so needed to kill some time before heading out. Happy Shooting!